During the past decades there have been considerable developments within the fields of radiation therapy and diagnosis. The performance of external beam radiation therapy accelerators, brachytherapy and other specialized radiation therapy equipment has improved rapidly. Developments taking place in the quality and adaptability of therapeutic radiation beams have included new targets and filters, improved accelerators, increased flexibility in beam-shaping through new applicators, collimator and scanning systems and beam compensation techniques. Also improved dosimetric and geometric treatment verification methods have been introduced. Furthermore, new treatment planing systems capable of biological optimization of the intensity distribution of the delivered beams are now being available.
In the field of multiple and single fraction radiation therapy and diagnostic imaging, a common general method is to position the patient on a couch. A radiation head and gantry are directing a diagnostic or therapeutic beam onto the patient in order to deliver radiation to a certain target or treatment volume, e.g. a tumor. Such a typical radiation machine according to the prior art is schematically illustrated in FIG. 1. The radiation machine comprises an isocentric gantry 80 designed in a general L shape and a rotational support provided at one axial end of the body of the machine for supporting the gantry 80. Thus, the gantry 80 can rotate around a rotation axis 30 relative the support in order to deliver a radiation beam, schematically illustrated by 10, from a radiation head 20 into a target volume 55 of a patient 50 positioned on a patient couch 40.
Most of the radiation therapy machines of today, including the machine in FIG. 1, comprise an isocentric gantry design. In such a design, the tissue or target volume 55 to be radiated is preferably positioned around a so-called isocenter typically formed by the intersection of three axes at a common point. These axes include the gantry rotation axis 30, the central axis of the radiation beam 10, the major rotational axis 45 of the treatment couch 45, which is also the rotation axis of the collimator head 20 in the figure.
A problem with such prior art radiation therapy machines is their limited capacity in terms of the total number of patients that can be treated in a given time interval. Although the actual irradiation is rather quick, i.e. it typically lasts a few minutes (1-2.5 minutes), a much longer treatment set-up normally precedes the irradiation. During such a set-up, the personnel positions the patient to be treated as accurately as possible, typically based on a treatment plan, which has been developed or compiled earlier based on diagnostic data, radiation beam data, etc. After placing the patient on the couch, but before the actual radiation therapy treatment, a treatment set-up is typically performed to test and verify the beam directions and the treatment plan. In the set-up procedure, the primary aim is setting up the equipment and patient according to the treatment plan. Often portal images, i.e. images based on the treatment beam itself, are used to verify the treatment and monitor its reproducibility. Furthermore, e.g. in vivo dosimetry or related techniques may be used to check the delivered radiation dose in the target volume and/or in adjacent tissues, particularly in organs at risk. If the measured data corresponds to the planed position in the treatment plan, the actual radiation therapy treatment may be safely initiated.
As a consequence of the patient set-up, positioning and simulation procedure, the total treatment takes considerably longer time, generally at least 5-10 minutes and often more, than the actual irradiation. In addition, if some divergence between the measured and calculated data is detected during the set-up and simulation and the divergence exceeds the tolerance margin, the treatment set-up should be adjusted. This may in some cases simply be a correction of some set-up parameters but also larger adjustments requiring a renewed treatment planning process with new anatomical information from a renewed diagnostic procedure. When, a new treatment plan is needed, a renewed treatment simulation may also be needed, increasing the time to treatment by a day or two.
Thus, the time, during which a radiation machine actually is employed for irradiating a patient, constitutes a small portion of the total time, during which the machine is occupied. This of course leads to poor utilization of the costly radiation machines and equipment and that fewer patients can be treated during a given period of time. This problem will be worsen further in cases where the patient undresses in the treatment room, the patient feels uncomfortable and wants to talk to the therapy assistants about various problems with the treatment, etc.
A possible solution could be to perform the simulation procedure using a dedicated radiation simulation machine and not the actual radiation treatment machine. However, although the designs of the patient couches and the two machines used for the simulation and the treatment, respectively, are similar, it may be more difficult to correctly simulate the treatment using a different machine and possibly a different couch top. This is due to problems with positioning the patient exactly in the same way on two different couches, even though the couches may have the same design. In addition, tissue and organs, including the target volume with a tumor, are deformable elastic structures and their positions relative to reference points used in the treatment plan are not rigid, but may change depending on e.g. posture of the patient, filling degree of bladder, respiratory motion, etc. Therefore, although the reference points may be aligned correctly during the treatment relative those during the simulation, the target volume may be misaligned.
In the patent specification U.S. Pat. No. 6,683,318, a therapy system adapted for cancer treatment using light ion radiation beams is disclosed. The therapy system includes an ion source providing light ions to an accelerator system including a synchrotron. An ion beam transport system guides an extracted high energy beam from the synchrotron into three different treatment rooms. In a first treatment room, a static gantry provides horizontal ion beam irradiation. In the remaining two treatment rooms, a respective rotatable isocentric gantry is arranged. Although, this therapy system is using a single ion source and beam accelerator system for the three gantries, the above-identified problems in terms of (low) patient throughput and cost-effectiveness are still present for the individual gantries of the therapy system.
Furthermore, many treatments with charged particles are not made using the isocentric set-up principle, such as during electron, proton or light ion therapy, where generally a fixed SSD treatment with fixed distance between source and patient surface is performed, making isocentric treatment units less important.